1. Field of the Invention
The present invention concerns a process for the removal of by-products from a phenolic mixture.
2. Description of Related Art
Phenol is commonly manufactured through a cumene procedure, wherein cumene is oxidized to cumene hydroperoxide (CHP) and the resulting oxidation product mixture is concentrated and subjected to a cleavage reaction. Subsequently, the cleavage product mixture is conducted to a distillation section, wherein the main products of the cleavage reaction, i.e. phenol and acetone, are first separated and then purified through a series of distillation steps or other purification steps. The crude phenol resulting from the separation of phenol and acetone contains several by-products, which are difficult or almost impossible to remove with conventional distillation. These by-products are for example α-methyl styrene (AMS), acetophenone residues, mesityl oxide and 2-methylbenzofurane.
Some of the mentioned by-products are insoluble in water and when mixed with phenol they may form heterogenic azeotropes. The boiling points of these azeotropes are generally in the same region as the boiling point of phenol, whereby their substantially complete removal with distillation is impossible.
Common phenol purification methods include hydroextraction (EP 0,505,146), extractive distillation (EP 0,571,042) and resin treatment (U.S. Pat. No. 5,414,154).
One more effective phenol purification procedure is a combination of a distillation and a resin treatment. A procedure of this type is presented in EP publications 1,395,540 and 1,727,779, wherein the phenol mixture to be purified is subjected to a resin treatment with an acidic resin, whereafter the product mixture is distilled to separate phenol from higher boiling compounds.
Since the resin treatment involves trapping by-products in a resin, which by-products deactivate the resin, the resin lifetime depends on the amount of by-products in the feed of the resin bed reactor. If, for example, the phenol to be purified has been manufactured through the above mentioned cumene oxidation and cleavage procedure, it may contain several different by-products, such as α-methyl styrene (AMS), hydroxyacetone, acetophenone residues, mesityl oxide, 2-methylbenzofurane, t-butyl benzene, cyclohexanol, phenyl dimethyl carbinol and other organic components, e.g. ketones and dimers. Since a large amount of by-products in the mixture results in a short lifetime for the resin and since a change of resin results in a stoppage of the phenol production, it would be advantageous to minimize the amount of by-products in the feed of the resin bed reactor.
One of the mentioned by-products is AMS, which is a water-insoluble compound formed from the oxidation by-product dimethyl phenyl carbinol (DMPC) by dehydration during the acid catalyzed cleavage of the main oxidation product CHP. AMS is a very reactive molecule, making it extremely harmful for a catalyst of the resin type, such as an ion exchange resin, since it causes catalyst deactivation.